QUANTIFYING THE EFFECT OF ROCK MASS QUALITY ON PEAK PARTICLE VELOCITY FOR UNDERGROUND DRIFT DEVELOPMENT

QUANTIFYING THE EFFECT OF ROCK MASS

QUALITY ON PEAK PARTICLE VELOCITY FOR

UNDERGROUND DRIFT DEVELOPMENT

by

Cristian Andres Caceres Doerner

A THESIS SUBMITTED IN PARTIAL FULLFILMENT OF

THE REQUIREMENTS FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

in

The Faculty of Graduate Studies

(Mining Engineering)

THE UNIVERSITY OF BRITISH COLUMBIA

(Vancouver)

December 2011

Cristian Andres Caceres Doerner, 2011

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ABSTRACT In prior research the existence of the strong relation between peak particle velocity

(PPV), as a result of blasting, and damage to civil structures and mining excavations has

been well established. In essence, the higher the PPV levels, the greater has been the

observed damage to a structure or excavation.

The first part of this thesis examines, through case studies in four underground mines, the

relationship observed between measured PPV and induced overbreak. These developed

relationships were established through a blast monitoring campaign of drift development

headings of markedly dissimilar rock mass qualities, varying from fair/poor to extremely

competent.

In the second part of this thesis is developed of a new methodology to estimate PPV,

which incorporates input parameters that are characteristic of different rock mass

qualities, such as propagation velocity and resonance frequency, and explosive

characteristics such as velocity of detonation (VOD). This methodology makes use of

waveforms to determine vibration levels from which the PPV of a blasthole is

established. The developed model estimates PPV by taking into consideration the spatial

location of the blasthole with respect to both the drift face, and the point of interest, and

the arrival time difference of every incremental charge (or packet) within a blasthole

based on the travel distance of the seismic wave, the VOD, and the rock mass propagation

velocities.

Current state of the art methodologies are solutions to a particular blasting situation; they

either consider a specific close range geometry, where they have limited applicability, or

they tend to be over simplified in the far-field by considering the explosive charge as a

point source. The proposed methodology considers a more realistic close range geometric

solution that can be applied specifically to a drifting situation, and improves some of the

drawbacks of current methodologies in the far-field range.

Finally, a more reliable estimation of PPV levels can help in the assessment of the

damage potential of a particular structure or excavation and therefore should help toward

preventive measures to make the working environment more safe and cost effective.

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TABLE OF CONTENTS Abstract.......................................................................................................................................ii Table of Contents ................................................................................................................... iii List of Tables ............................................................................................................................vi List of Figures......................................................................................................................... vii List of Abbreviations and Symbols..................................................................................xvi Acknowledgements..............................................................................................................xix Dedication ................................................................................................................................xx 1 Introduction........................................................................................................................1 1.1 Motivation and Significance of the Proposed Research............................................ 1 1.2 Scope and Objective .............................................................................................................. 2 1.3 Methodology ............................................................................................................................ 3 1.4 Statement of Contributions ................................................................................................ 5 1.5 Thesis Outline ......................................................................................................................... 6

2 Literature Research .........................................................................................................9 2.1 Falls of Ground A Latent Threat to Miners ................................................................. 9 2.2 Ground Vibrations and Damage Assessment .............................................................11 2.2.1 Introduction .................................................................................................................................... 11 2.2.2 Beyond the Detonation Process.............................................................................................. 13 2.2.3 The Harmonic Seismic Wave Equation ............................................................................... 16 2.2.4 Seismic Wave Attenuation ........................................................................................................ 18 2.2.5 Seismic Wave Diffraction........................................................................................................... 19 2.2.6 Seismographs ................................................................................................................................. 19 2.2.7 Geophone Damping...................................................................................................................... 20 2.2.8 Frequency of Vibration............................................................................................................... 21 2.2.9 Frequency Spectrum ................................................................................................................... 21 2.2.10 Scaling and Prediction of Ground Vibrations................................................................. 22 2.2.11 Rock Mass Damage from Blasting....................................................................................... 30 2.2.12 Particle Velocity Estimates in Relation to Structural Damage................................ 32 2.2.13 Blast Damage Measurement Techniques......................................................................... 32 2.2.14 Blast Overbreak .......................................................................................................................... 33 2.3 Rock Mass Classification....................................................................................................34 2.3.1 Introduction .................................................................................................................................... 34 2.3.2 Bieniawskis Geomechanics Classification - RMR ........................................................... 37 2.3.3 Bartons Rock Tunneling Quality Index, Q ......................................................................... 38 2.3.4 Rock Support Under Dynamic Loading ............................................................................... 42 2.3.5 Support Design Requirements ................................................................................................ 43

3 Field Data Collection and Analysis........................................................................... 44 3.1 Introduction...........................................................................................................................44 3.2 The Drifting Process ...........................................................................................................44 3.3 Methods of Field Data Collection ....................................................................................45 3.3.1 Process of Field Data Collection ............................................................................................. 45 3.3.2 Rock Mass Quality Assessments............................................................................................. 47 3.3.3 Blast Monitoring and Equipment........................................................................................... 50

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3.3.4 Explosives Characteristics ........................................................................................................ 55 3.4 Methods of Analysis of Field Data ..................................................................................56 3.4.1 PPV and SD ....................................................................................................................................... 56 3.4.2 Frequency Content of a Waveform........................................................................................ 58 3.4.3 PPV Analysis using Band-Pass Filter .................................................................................... 58 3.4.4 Data Processing ............................................................................................................................. 60 3.4.5 Overbreak Assessments Scanner Profiles ...................................................................... 65 3.4.6 Other Analysis of Field Data..................................................................................................... 68 3.4.7 Structural Mapping ...................................................................................................................... 69 3.4.8 Detonator Delay Scatter............................................................................................................. 70 3.5 Limitations and Advantages of the Presented Empirical Data .............................72

4 Case Studies ..................................................................................................................... 74 4.1 Introduction...........................................................................................................................74 4.2 Stillwater Mine Montana USA .......................................................................................75 4.2.1 Rock Mass Quality......................................................................................................................... 76 4.2.2 Vector Sum PPV and Frequency Content............................................................................ 81 4.3 SSX-Steer Mine Nevada USA ..........................................................................................84 4.3.1 Rock Mass Quality......................................................................................................................... 84 4.3.2 Vector Sum PPV and Frequency Content............................................................................ 89 4.4 Turquoise Ridge JV Mine Nevada USA .......................................................................93 4.4.1 Rock Mass Quality......................................................................................................................... 94 4.4.2 Vector Sum PPV and Frequency Content............................................................................ 98 4.5 Musselwhite Mine Ontario Canada .......................................................................... 102 4.5.1 Rock Mass Quality.......................................................................................................................102 4.5.2 Vector Sum PPV and Frequency Content..........................................................................106 4.6 Analysis of Results............................................................................................................ 110 4.6.1 PPV versus SD for a Wide Range of Rock Mass Qualities...........................................110 4.6.2 Charge Weight per Delay .........................................................................................................113

5 PPV Modeling The Proposed Methodology ......................................................115 5.1 Introduction........................................................................................................................ 115 5.2 The Semi Empirical Modeling Tool ............................................................................. 116 5.2.1 Background ...................................................................................................................................116 5.2.2 Model Set-Up.................................................................................................................................118 5.2.3 Point of Diffraction (POD) .......................................................................................................119 5.2.4 Assumptions..................................................................................................................................121 5.2.5 Analytical Background..............................................................................................................123 5.3 Arrival Time Analysis ...................................................................................................... 127 5.3.1 General ............................................................................................................................................127 5.3.2 Stress Wave Propagation Velocity Rock Mass Quality Dependence .................130 5.3.3 Arrival Time Rock Mass Sound Velocity Dependence.............................................132 5.4 Particle Velocity Analysis Drifting Case ................................................................. 141 5.4.1 Proposed PPV Equation Analytical Background........................................................141 5.4.2 Determination of Constants ...................................................................................................144 5.4.3 Waveform Generation Frequency Dependence .........................................................145 5.4.4 Phase Shift - Delayed Arrival Times of Peak Velocities ..............................................147 5.4.5 Resonance Vibration Frequency Range of a Rock Mass Medium ..........................157 5.4.6 Model Sampling Rate.................................................................................................................159 5.5 PPV Diffraction Case...................................................................................................... 163 5.5.1 General ............................................................................................................................................163

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5.5.2 Arrival Time Two Blastholes with identical Nominal Delay.................................171 5.6 PPV for Practical Cases.................................................................................................... 173 5.6.1 General ............................................................................................................................................173 5.6.2 Competent Rock Mass Good Rock Mass Quality; RMR > 75..................................174 5.6.3 Weak Rock Mass Poor/Fair Rock Mass Quality; RMR > 35 ...................................180

6 Model Testing................................................................................................................186 6.1 Field Data PPV Measurements Musselwhite Mine Case.................................... 186 6.2 PPV Data Measured versus Modeled Musselwhite Mine Case ........................ 191

7 Applications of the Proposed Model......................................................................197 7.1 General ................................................................................................................................. 197 7.2 Analysis of the PPV for different Explosive Types ................................................. 197 7.3 Blasthole Interaction Analysis ..................................................................................... 204 7.4 Other Applications of the Model .................................................................................. 206 7.4.1 Blasthole Distribution Analysis ............................................................................................206 7.4.2 Surface and Underground Blasts .........................................................................................206 7.4.3 Pyrotechnic Caps Delay Scatter ............................................................................................207 7.5 Limitations of the Model................................................................................................. 207

8 Conclusions ....................................................................................................................209 9 Recommended Future Work....................................................................................214 References.............................................................................................................................216 Appendices............................................................................................................................223 Appendix A Rock Mass Quality Logs..........................................................................223 Appendix B Particle velocity and Frequency Content - Case Studies .............247

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LIST OF TABLES Table 2.1 Rock Mass Rating System (After Bieniawski, 1976) ....................................... 38 Table 2.2 Classification of individual parameters used in the Tunneling

Quality Index Q (After Barton et al 1974)................................................................ 40 Table 3.1 High Frequency Triaxial Geophone Instruction Sheet (source:

www.instantel.com, June 2011)................................................................................ 53 Table 3.2 Explosive utilized Main specifications (source:

www.dynonobel.com, June 2011) ............................................................................ 55 Table 4.1 Mine site case studies ....................................................................................... 74 Table 4.2 Number of PPV measurements and average RMR ........................................... 75 Table 4.3 Bartons Q index components Stillwater Mine.............................................. 78 Table 4.4 Bieniawskis RMR ratings Stillwater Mine ................................................... 79 Table 4.5 Summary of blasthole ID, explosive types and relative weights

per blasthole Stillwater Mine ................................................................................. 79 Table 4.6 Bartons Q index components SSX Mine...................................................... 87 Table 4.7 Bieniawskis RMR ratings SSX Mine............................................................ 87 Table 4.8 Summary of explosive ID, types and relative weights per

blasthole SSX Mine ............................................................................................... 89 Table 4.9 Bartons Q index components Turquoise Ridge JV Mine............................. 96 Table 4.10 Bieniawskis RMR ratings Turquoise Ridge JV Mine................................. 96 Table 4.11 Summary of explosive ID, types and relative weights per

blasthole Turquoise Ridge JV Mine ...................................................................... 97 Table 4.12 Bartons Q index components Musselwhite Mine..................................... 105 Table 4.13 Bieniawskis RMR ratings Musselwhite Mine........................................... 105 Table 4.14 Summary of explosive ID, types and relative weights per

blasthole Musselwhite Mine ................................................................................ 105 Table 5.1 Table of propagation velocities for different mediums (source:

Pavlovic, 1998) ....................................................................................................... 131 Table 5.2 Table of explosive detonation velocities ........................................................ 133

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LIST OF FIGURES Figure 2.1 Percentage of underground mining injuries in U.S. classified by

accident type (source: U.S. Department of Labor: Bureau of Labor Statistics (http://www.bls.gov/iif/, June 2011)) .......................................................... 9

Figure 2.2 Percentage of underground mining fatalities in U.S. classified by accident type (source: U.S. Department of Labor: Bureau of Labor Statistics (http://www.bls.gov/iif/, June 2011)) ........................................................ 10

Figure 2.3 Fall of ground related injuries in U.S. (source: U.S. Department of Labor: Bureau of Labor Statistics (http://www.bls.gov/iif/, June 2011)) ........................................................................................................................ 11

Figure 2.4 Detonation velocity for ANFO versus charge diameter (modified from source: Rock Blasting and Explosives Engineering pg. 101)....................... 15

Figure 2.5 Integration of the surface wave effect in the near region of an extended charge (After Persson et. al., 2001) pg. 245 .............................................. 28

Figure 2.6 ELOS concept to measure average stope overbreak........................................ 34 Figure 2.7 Procedure for measurement and calculation of RQD (after

Deere, 1989).............................................................................................................. 36 Figure 3.1 Sequential tasks of the drifting process ........................................................... 45 Figure 3.2 Pre-blast data collection process ..................................................................... 46 Figure 3.3 Post-blast data collection process .................................................................... 46 Figure 3.4 Relationship between discontinuity spacing and RQD, after

Bieniawski (1989)..................................................................................................... 48 Figure 3.5 Cell mapping of both walls and back for each round...................................... 49 Figure 3.6 Photograph of the left wall showing structures and rock mass

condition ................................................................................................................... 50 Figure 3.7 Protective metal box with geophone and datalogger installed ........................ 51 Figure 3.8 Minimate Plus and high frequency triaxial geophone.................................. 52 Figure 3.9 SM-7 30Hz geophone response curve (modified from

www.iongeo.com, June 2011) .................................................................................. 54 Figure 3.10 SM-7 30Hz geophone phase lag (modified from

www.iongeo.com, June 2011) .................................................................................. 55 Figure 3.11 Perimeter and lifter blastholes - Explosives distribution

Stillwater mine .......................................................................................................... 57 Figure 3.12 PPV versus time record With and without band pass filter (0-

100Hz)....................................................................................................................... 58 Figure 3.13 PPV versus time record With and without band pass filter

(100-500Hz).............................................................................................................. 59 Figure 3.14 PPV versus time record With and without band pass filter

(500-1000Hz)............................................................................................................ 59 Figure 3.15 PPV versus time record With and without band pass filter

(1000-1500Hz).......................................................................................................... 60 Figure 3.16 Transversal, vertical and longitudinal particle velocity record ..................... 61 Figure 3.17 Vector sum of the three individual particle velocity

components ............................................................................................................... 62 Figure 3.18 Isolated seismic waveform ............................................................................ 63

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Figure 3.19 Frequency content for burn cut blasthole ...................................................... 63 Figure 3.20 Planned or as-built profile against final profile ............................................. 65 Figure 3.21 Average overbreak measurement over an entire blasted round

section ....................................................................................................................... 66 Figure 3.22 Leica HDS3000 laser scanner................................................................. 67 Figure 3.23 Laser scanned profile of a development drift ................................................ 68 Figure 3.24 Picture of the face showing dimensions and blasthole long

period delay number ................................................................................................. 69 Figure 3.25 Representation of major structures on Schmidt stereonet ............................. 70 Figure 3.26 Long period cap delay scatter........................................................................ 71 Figure 3.27 PPV versus SD............................................................................................... 72 Figure 4.1 4400ft level heading plan view Stillwater Mine........................................ 76 Figure 4.2 Typical 4400ft and 4700ft level headings support installed

Stillwater Mine.......................................................................................................... 77 Figure 4.3 4400ft level heading blocky ground with support Stillwater

Mine .......................................................................................................................... 77 Figure 4.4 4400ft level headings after-blast picture Stillwater Mine ......................... 78 Figure 4.5 Typical 4400ft and 4700ft level headings blast pattern

Stillwater Mine.......................................................................................................... 80 Figure 4.6 4400ft elevation heading Laser scanned side view SSX Mine.................. 81 Figure 4.7 PPV versus time Stillwater Mine ................................................................. 81 Figure 4.8 PPV versus SD values Stillwater Mine ........................................................ 82 Figure 4.9 PPV versus SD boundary 95% confidence level Stillwater

Mine .......................................................................................................................... 83 Figure 4.10 Frequency content Stillwater Mine ............................................................ 84 Figure 4.11 7170 cross cut XC11 level heading plan view SSX Mine....................... 85 Figure 4.12 Rock mass appearance & support installed of right wall SSX

Mine .......................................................................................................................... 86 Figure 4.13 Rock mass appearance adjacent to zone under study SSX

Mine .......................................................................................................................... 86 Figure 4.14 XC11 heading blast pattern SSX Mine ................................................... 88 Figure 4.15 XC11 heading Laser scanned view SSX Mine........................................ 89 Figure 4.16 PPV versus time SSX Mine........................................................................ 90 Figure 4.17 PPV versus SD values SSX Mine............................................................... 91 Figure 4.18 PPV versus SD boundary 95% confidence level SSX Mine ................... 92 Figure 4.19 Frequency content SSX Mine..................................................................... 93 Figure 4.20 3471 development panel plan view Turquoise Ridge JV

Mine .......................................................................................................................... 94 Figure 4.21 Rock mass at face and support Turquoise Ridge JV Mine......................... 95 Figure 4.22 Rock mass at upper corner After-blast picture Turquoise

Ridge JV Mine .......................................................................................................... 95 Figure 4.23 Shotcreted walls Pre-blast picture Turquoise Ridge JV

Mine .......................................................................................................................... 96 Figure 4.24 3471 development heading blast pattern Turquoise Ridge

JV Mine..................................................................................................................... 98 Figure 4.25 PPV versus time Turquoise Ridge JV Mine.............................................. 99

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Figure 4.26 PPV versus SD values Turquoise Ridge JV Mine.................................... 100 Figure 4.27 PPV versus SD boundary 95% confidence level Turquoise

Ridge JV Mine ........................................................................................................ 101 Figure 4.28 Frequency content Turquoise Ridge JV Mine.......................................... 102 Figure 4.29 720L C Block East plan view Musselwhite Mine .................................... 103 Figure 4.30 720L C Block East face and drill pattern Musselwhite Mine .................. 103 Figure 4.31 720L C Block East rock mass and rebar bolts pattern

Musselwhite Mine................................................................................................... 104 Figure 4.32 720L C Block East back support with rebar and mesh

Musselwhite Mine................................................................................................... 104 Figure 4.33 720L C Block East heading blast pattern Musselwhite Mine ............... 106 Figure 4.34 PPV versus time Musselwhite Mine....................................................... 107 Figure 4.35 PPV versus SD values Musselwhite Mine................................................ 108 Figure 4.36 PPV versus SD boundary 95% confidence level

Musselwhite Mine................................................................................................... 109 Figure 4.37 Frequency content Musselwhite Mine...................................................... 110 Figure 4.38 PPV versus SD for a range of rock mass qualities ...................................... 111 Figure 4.39 PPV versus SD. Solid lines represents 95% confidence level..................... 111 Figure 4.40 PPV versus SD Log scale for a range of rock mass qualities ................ 112 Figure 4.41 Log(PPV) versus Log(SD) for a range of rock mass qualities ................. 113 Figure 4.42 Delay time scatter Pyrotechnic blasting caps ........................................... 114 Figure 5.1 2D representation of a blast pattern............................................................... 117 Figure 5.2 Three dimensional projection of the blasthole locations ............................... 118 Figure 5.3 Packet representation and location of a centroid ........................................... 119 Figure 5.4 Point of diffraction height ZPOD of multiple packets ..................................... 120 Figure 5.5 Incidence, reflected and diffracted/refracted rays ......................................... 120 Figure 5.6 Packet initiation sequence Expanding seismic wavefront and

ray path.................................................................................................................... 122 Figure 5.7 Point of diffraction height ZPOD nth and angle of incidence nth of

nth packet ................................................................................................................. 124 Figure 5.8 Point of diffraction height ZPOD ith and angle of incidence ith of

ith packet .................................................................................................................. 125 Figure 5.9 Ascending arrival times from the initiation point (Packet 17) ...................... 128 Figure 5.10 Descending arrival times from the initiation point (Packet 17) .................. 128 Figure 5.11 Parabolic ascending arrival times from the initiation point

(Packet 17) .............................................................................................................. 129 Figure 5.12 Parabolic arrival times. Central packets of the wavefront

arrives first .............................................................................................................. 129 Figure 5.13 Simultaneous arrival times for all packets................................................... 130 Figure 5.14 P-wave velocity (m/s) for various rock types (modified from

source: http://science.jrank.org/pages/48110/seismic-properties-rocks.html, January 2011)....................................................................................... 132

Figure 5.15 Arrival times for highlighted blasthole location.......................................... 133 Figure 5.16 Arrival times Vbw=6500m/s Good rock quality Y=0.9m

Z=0.0m.................................................................................................................... 136

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Figure 5.17 Arrival times Vbw=6500m/s Good rock quality Y=0.0m Z=0.0m.................................................................................................................... 136




Figure 5.21 Arrival times Vbw=2000m/s Poor/Fair rock quality Y=0.9m Z=0.0m .................................................................................................... 138





Figure 5.26 User defined modeling parameters flowchart.............................................. 142 Figure 5.27 Initial calculations flowchart ....................................................................... 143 Figure 5.28 Model waveform generation........................................................................ 143 Figure 5.29 Model PPV determination from linear superposition of

multiple waveforms ................................................................................................ 144 Figure 5.30 High frequency; Packets arrive simultaneously Zero phase

shift ......................................................................................................................... 146 Figure 5.31 Low frequency; Packets arrive simultaneously Zero phase

shift ......................................................................................................................... 146 Figure 5.32 Waveform time shift between two packets ................................................. 147 Figure 5.33 Discrete Hustrulid-Lu values and continuous modeled

waveforms............................................................................................................... 148 Figure 5.34 High frequency waveform; PPV modeled versus PPV from

Hustrulid-Lu equation (2000) Zero phase shift ................................................... 149 Figure 5.35 Low frequency waveform; PPV modeled versus PPV from

Hustrulid-Lu equation (2000) Zero phase shift ................................................... 150 Figure 5.36 High Velocity and Frequency; PPV modeled vs. PPV from

Hustrulid-Lu equation Vexplosive=10,000m/s....................................................... 151 Figure 5.37 Low Velocity and Frequency; PPV modeled vs. PPV from

Hustrulid-Lu equation Vexplosive=10,000m/s....................................................... 151 Figure 5.38 High Velocity and Frequency; PPV modeled vs. PPV from

Hustrulid-Lu equation Vexplosive=8,250m/s......................................................... 152 Figure 5.39 Low Velocity and Frequency; PPV modeled vs. PPV from

Hustrulid-Lu equation Vexplosive=8,250m/s......................................................... 152 Figure 5.40 High Velocity and Frequency; PPV modeled vs. PPV from

Hustrulid-Lu equation Vexplosive=6,500m/s......................................................... 153 Figure 5.41 Low Velocity and Frequency; PPV modeled vs. PPV from

Hustrulid-Lu equation Vexplosive=6,500m/s......................................................... 153

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Figure 5.42 High Velocity and Frequency; PPV modeled vs. PPV from Hustrulid-Lu equation Vexplosive=5,000m/s......................................................... 154

Figure 5.43 Low Velocity and Frequency; PPV modeled vs. PPV from Hustrulid-Lu equation Vexplosive=5,000m/s......................................................... 154





Figure 5.48 Waveforms generated at various frequency ranges..................................... 158 Figure 5.49 Linear superposition of waveforms generated at various

frequency ranges ..................................................................................................... 159 Figure 5.50 Model sampling rate = 500,000Hz .............................................................. 161 Figure 5.51 Model sampling rate = 25,000Hz ................................................................ 161 Figure 5.52 Model sampling rate = 16,384Hz ................................................................ 162 Figure 5.53 Model sampling rate = 8,192Hz .................................................................. 162 Figure 5.54 Model sampling rate = 4,096Hz .................................................................. 163 Figure 5.55 Arrival times Signature blasthole case ..................................................... 166 Figure 5.56 PPV waveforms for selected packets Signature blasthole case................ 166 Figure 5.57 PPV waveforms for all 17 packets Signature hole case ........................... 167 Figure 5.58 Linear superposition of individual PPV waveforms Signature

blasthole case .......................................................................................................... 167 Figure 5.59 Arrival times Diffraction case .................................................................. 169 Figure 5.60 PPV waveforms for selected packets Diffraction case............................. 169 Figure 5.61 PPV waveforms for all 17 packets Diffraction case................................. 170 Figure 5.62 Linear superposition of individual PPV waveforms

Diffraction case....................................................................................................... 170 Figure 5.63 Arrival times for two blastholes at different locations Zero

time scatter .............................................................................................................. 172 Figure 5.64 Linear superposition between 2 blastholes with same delay

number .................................................................................................................... 173 Figure 5.65 Arrival times and PPV for highlighted blasthole location........................... 174 Figure 5.66 Good rock mass quality PPV vs. time waveform Record &

model....................................................................................................................... 175 Figure 5.67 Arrival times - Good rock mass quality case - Y=0.0 Z = -1.73 ................. 176 Figure 5.68 Particle velocity waveforms - Good rock mass quality case -

Y=0.0 Z = -1.73 ...................................................................................................... 177 Figure 5.69 Linear superposition - Good rock mass quality case - Y=0.0 Z

= -1.73 ..................................................................................................................... 178 Figure 5.70 Arrival times - Good rock mass quality case - Y=3.5 Z = -1.73 ................. 179 Figure 5.71 Particle velocity waveforms - Good rock mass quality case -

Y=3.5 Z = -1.73 ...................................................................................................... 179

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Figure 5.72 Linear superposition - Good rock mass quality case - Y=3.5 Z = -1.73 ..................................................................................................................... 180

Figure 5.73 Fair/Poor rock mass quality PPV vs. time waveform Record & model ...................................................................................................... 181

Figure 5.74 Arrival times - Poor/Fair rock mass quality case - Y=0.0 Z = -1.73.......................................................................................................................... 182

Figure 5.75 Particle velocity waveforms - Poor/Fair rock mass quality case - Y=0.0 Z = -1.73 .................................................................................................... 183

Figure 5.76 Linear superposition - Poor/Fair rock mass quality case - Y=0.0 Z = -1.73 ...................................................................................................... 183

Figure 5.77 Arrival times - Poor/Fair rock mass quality case - Y=3.5 Z = -1.73.......................................................................................................................... 184

Figure 5.78 Particle velocity waveforms - Poor/Fair rock mass quality case - Y=3.5 Z = -1.73 .................................................................................................... 185

Figure 5.79 Linear superposition - Poor/Fair rock mass quality case - Y=3.5 Z = -1.73 ...................................................................................................... 185

Figure 6.1 Blastholes location and linear charge density .............................................. 188 Figure 6.2 Measured PPV values Musselwhite Mine 9.5m from the face ............... 189 Figure 6.3 Measured PPV values Musselwhite Mine 10.5m from the

face.......................................................................................................................... 190 Figure 6.4 Measured PPV values Musselwhite Mine 21.5m from the

face.......................................................................................................................... 190 Figure 6.5 Measured PPV values Musselwhite Mine 26.6m from the

face.......................................................................................................................... 191 Figure 6.6 Measured versus modeled PPV surface contours 9.5m from

the face .................................................................................................................... 192 Figure 6.7 Surface projection of modeled surface contours 9.5m from the

face.......................................................................................................................... 192 Figure 6.8 Measured versus modeled PPV surface contours 10.5m from

the face .................................................................................................................... 193 Figure 6.9 Surface projection of modeled surface contours 10.5m from

the face .................................................................................................................... 193 Figure 6.10 Measured versus modeled PPV surface contours 21.5m from


the face .................................................................................................................... 194 Figure 6.12 Measured versus modeled PPV surface contours 26.5m from


the face .................................................................................................................... 195 Figure 7.1 Near-field PPV of ANFO............................................................................... 199 Figure 7.2 Near-field PPV of ANFO Finer discretization around the

blasthole .................................................................................................................. 199 Figure 7.3 Near-field PPV modeled 3D surface SEC Detagel ............................. 201 Figure 7.4 Near-field PPV modeled 2D projection SEC Detagel......................... 201 Figure 7.5 Near-field PPV modeled 3D surface ANFO............................................ 202

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Figure 7.6 Near-field PPV modeled 2D projection ANFO ....................................... 202 Figure 7.7 Near-field PPV modeled 3D surface Dyno AP ................................... 203 Figure 7.8 Near-field PPV modeled 2D projection Dyno AP............................... 203 Figure 7.9 Blasthole Interaction 3D surface Dyno AP ......................................... 205 Figure 7.10 Blasthole Interaction 2D projection Dyno AP................................... 205 Figure 7.11 Application to a surface blast situation ....................................................... 207

Figure A. 1 Back, right and left wall pictures and rock mass classification logs Stillwater Mine Cross cut 1....................................................................... 223



Figure A. 4 Back, right and left wall pictures and rock mass classification logs Stillwater Mine Footwall lateral 1............................................................. 226





Figure A. 9 Back, right and left wall rock mass classification logs Stillwater Mine Footwall lateral 6 ....................................................................... 231

Figure A. 10 Back, right and left wall rock mass classification logs Stillwater Mine Footwall lateral 7 ....................................................................... 231



Figure A. 13 Back, right and left wall pictures and rock mass classification logs Stillwater Mine Footwall lateral 10........................................................... 234






Figure A. 19 Back, right and left wall pictures and rock mass classification logs SSX Mine Cross cut 11-1.......................................................................... 240

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Figure A. 24 Back, right and left wall pictures and rock mass classification logs Musselwhite Mine Footwall lateral 1........................................................ 245

Figure A. 25 Back, right and left wall rock mass classification logs Turquoise Ridge JV Mine Footwall lateral 1....................................................... 246

Figure B. 1 Particle velocity record Transversal, vertical and longitudinal Musselwhite Mine................................................................................................ 247

Figure B. 2 Particle velocity record Transversal, vertical and longitudinal Stillwater Mine..................................................................................................... 248

Figure B. 3 Particle velocity record Transversal, vertical and longitudinal Turquoise Ridge JV Mine.................................................................................... 249

Figure B. 4 Particle velocity record Transversal, vertical and longitudinal SSX Mine............................................................................................................. 250

Figure B. 5 Original (Trans1) and truncated transversal particle velocity records (Trun1) Musselwhite Mine ..................................................................... 251

Figure B. 6 Frequency content of original (Trans1) and truncated transversal particle velocity records (Trun1) Musselwhite Mine ........................ 252

Figure B. 7 Frequency content of truncated unsmoothed and smoothed (average of 2, 3, 4, 5, 6 and 7 consecutive samples) transversal particle velocity records Musselwhite Mine ..................................................................... 253

Figure B. 8 Frequency content of truncated unsmoothed and smoothed (average of 8 consecutive samples) transversal particle velocity records Musselwhite Mine................................................................................... 254

Figure B. 9 Frequency content of truncated unsmoothed and smoothed blast and quiet portion (average of 4 and 8 consecutive samples) of the transversal particle velocity records Musselwhite Mine...................................... 255

Figure B. 10 Frequency content of transversal, vertical and longitudinal particle velocity records #0 delay Stillwater Mine ........................................... 256

Figure B. 11 Frequency content of transversal, vertical and longitudinal particle velocity records #2 (1/2) delay Stillwater Mine .................................. 257





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Figure B. 27 Frequency content of transversal, vertical and longitudinal particle velocity records #11 delay Stillwater Mine ......................................... 273




Figure B. 31 Frequency content of transversal, vertical and longitudinal particle velocity records #15 (1/2) delay Stillwater Mine ................................ 277

Figure B. 32 Frequency content of transversal, vertical and longitudinal particle velocity records #15 (2/2) delay Stillwater Mine ................................ 278

Figure B. 33 Frequency content of transversal, vertical and longitudinal particle velocity records #1 delay at 9.5m from face Musselwhite Mine ........................................................................................................................ 279




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LIST OF ABBREVIATIONS AND SYMBOLS a - Acceleration

A - Amplitude

ANFO - Ammonium nitrate and fuel oil

c - Characteristic propagation velocity of P/S/Raleigh wave

CMRI - Central Mining Research Institute

d - Displacement

D - Distance

E - Original energy stored in a wave

ELOS - Equivalent linear overbreak slough

ER - Energy ratio

f - Frequency

fdom - Dominant frequency

FFT - Fast Fourier transform

GPR - Ground penetrating radar

HCF - Half cast factor

ISP - Indian Standard Predictor

Ja - Joint alteration number

Jn - Joint set number

Jr - Joint roughness number

Jv - Volumetric joint count

Jw - Joint water reduction factor

l - Linear charge concentration

LIDAR - Light Detection and Ranging

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NIOSH - National Institute for Occupational Safety and Health

POD - Point of diffraction

PPV - Peak particle velocity

Q - Bartons rock tunnelling quality index

QE - Mass of explosive charge

Qf - Quality factor

RMR - Bieniawski's rock mass rating

RQD - Deeres rock quality designation

SD - Scaled distance

SRF - Stress reduction factor

t - Time

T - Period

TDR - Time domain reflectometry

u - Harmonic displacement

USBM - U.S. Bureau of Mines

V - Velocity

VP - Particle velocity

VOD - Velocity of detonation

ZPOD - Z coordinate at the point of diffraction

P - P-Wave velocity

ith - Angle formed between the ith packet (elemental charge) and the horizontal

S - S-Wave velocity

E - Energy lost in one cycle

- Strain

xviii

- longitudinal shear displacement vector

- Wavelength

- rotational shear displacement vector

- angular frequency

- phase shift

xix

ACKNOWLEDGEMENTS I would like to thank the committee members for all the support they gave me throughout

all these years without which it would have been impossible to complete this research and

thesis. My greatest thanks goes to my supervisor Dr. Rimas Pakalnis for the immense and

invaluable amount of knowledge he has shared with me, for his trust and friendship,

patience and financial support.

To my co-supervisor Dr. Michael Hitch for his editing support and his exchange of

knowledge and ideas, which improved my research findings and helped to produce a

better thesis document.

To Dr. Malcolm Scoble for his directions and detailed assessment of my research and his

key and precise editing contributions.

To Dr. Scott Dunbar and David Sprott for their supervision and fundamental directions.

The author would like to thank immensely NIOSH Spokane Research Laboratory and the

blasting research team for their financial support, and their contribution of knowledge, as

well as the support of their qualified personnel, these being fundamental components in

the completion of this research. They have also made available their state of the art

equipment and assisted in the organization of the field investigations. The author is

particularly grateful to the following: Jami Dwyer, Steve Iverson, Bill Hustrulid, Ed

McHugh, Ted Williams, Tom Brady, and Joel Warneke.

To Trent McColl for his editorial support. With his English expertise, the thesis is now

much more comprehensible as before.

The author would also like to thank the following mining companies and their personnel

involved: Stillwater Mining Company, Queenstake Resources, Barrick Gold Corp. and

Newmont Mining Corp., and Goldcorp Inc.. They provided invaluable assistance during

the data acquisition phase of the research, and allowed the use of their time, facilities, and

equipment, without which this research could not have been conducted.

xx

DEDICATION

To my wife Veronica and my daughters Victoria and Javiera and to my son Tomas. To

my parents Ximena and Alberto. To my family and friends. They all gave me the strength

and confidence necessary to pursue this incredible endeavor.

1

1 INTRODUCTION

1.1 Motivation and Significance of the Proposed Research Since the beginning of the twentieth century, more than 50,000 mining related fatalities

have occurred in the U.S. alone (which is approximately half of all fatalities in metal and

non-metal mining, excluding coal), according to NIOSHs Information Circular 9520

(Breslin, 2010). A significant portion of these fatalities would be related to ground falls

and pillar failures. According to the U.S. Department of Labor, the incidence of fatal

injuries fell dramatically during the period 2006 to 2010 (31 fatalities total due to

face/rib/highwall falls of roof and back, pertaining to both surface and underground

mining). Reducing fatalities and injuries across the mining industry remains a principle

concern.

A strong relationship between peak particle velocity (PPV) as a result of blasting and

damage to civil structures and mining excavations has been well established by previous

research. In essence, the higher the PPV, the greater the observed damage to a structure

or excavation. Estimating PPV levels occurring at any given location (with respect to the

explosive charge) as accurately as possible thus becomes critical toward making better,

more reliable predictions of the potential for damage to existing structures and

excavations.

The primary motivation of this research is to make the drifting process safer by

preventing injuries and fatalities from roof and rib falls in underground mines. The

triggering of these failures can have diverse origins but one major factor is the excessive

vibration levels resulting from blasting.

In addition, this research aims to make the drifting process more cost effective by

ensuring a better understanding of the working environment, in terms of particle velocity,

which has the potential to cause rock instabilities, as a result of the blasting process. From

a geotechnical perspective, cost effective solutions are reached when support designs can

prevent all potential instabilities from occurring at the minimum possible cost. Hence, if

this process can establish a reliable estimation of the maximum vibration levels, and

2

therefore, an estimate of the degree of damage caused by blasting, then there will be

advances in the optimization of drift support designs.

1.2 Scope and Objective The information produced by this research can be used by geotechnical and blasting

personnel for a more comprehensive analysis of a particular situation, as this information

relates to various rock mass conditions existing at their sites. This research provides

empirical relationships relating PPV, scaled distance (SD), and overbreak obtained

throughout the analysis of data gathered. Mine sites were selected in order to cover a

broad range of rock mass qualities assessed in terms of RMR and Q, ranging from

fair/poor to extremely competent.

In the authors opinion, there is a lack of tools available to the geotechnical and blasting

community that can be used to determine PPV, specifically in a drifting situation. The

existing tools produce overly simplistic solutions, which can lead to large calculation

errors in PPV value estimation. This research is oriented to the geotechnical and blasting

personnel who are engaged in analysis of the stability of development drifts. The

proposed methodology, which has been developed specifically for a drifting situation, can

have positive impacts in the reduction of underground rock failure. This methodology

considers important geometric and geophysical features not necessarily addressed by

traditional methodologies. Moreover, the methodology is also applicable to surface and

underground production blasting when the surface layout is similar to that existing in drift

development.

The proposed methodology has been verified experimentally using a modeling tool

developed and tested with commonly used spreadsheet software and is presented by the

author to be more accurate than current methodologies, as it incorporates parameters that

are characteristic of the quality of the rock mass and the explosives utilized.

The main objective is the development of a new methodology and modeling tool that,

once calibrated, can be used by the blasting engineer to improve and optimize designs of

blasting rounds. A reliable estimation of the PPVs determined at any given location, some

distance from the blast or within the blast round, can then be related to the potential for

3

overbreak and damage occurring at these locations and can therefore assess the potential

risk to mining personnel.

1.3 Methodology A total of four underground mines located in North America were investigated, and their

drill and blast operations monitored with respect to blasthole location, explosive

distribution, delay sequence, seismic vibration monitoring, ground support employed,

overbreak assessment, and rock mass quality assessment. Each of the four sites

investigated showed clear differences with respect to the other three, in that the sites

exhibit a broad range of rock mass qualities, all of which were subsequently analyzed in

terms of measured PPV and the associated frequency content. Two widely used rock

mass classification systems to assess rock mass quality were employed at the mine sites

investigated. These are Bieniawski's Rock Mass Rating, RMR (1976) and Bartons Rock

Tunnelling Quality Index, Q (1974).

The seismic records of particle velocity versus time were recorded via high-frequency

geophones and dataloggers that were installed along the walls of the monitored drifts,

some distance from the blast.

Measurements of blast-induced overbreak were estimated from laser scanner profiles and

planned surface of excavation. A less accurate method using a handheld laser distance

meter was also employed to estimate overbreak in those situations where laser scanner

equipment was not available.

Site-specific characteristic curves were then obtained from the records of PPV versus SD

data. These site-specific characteristic curves present further evidence that as rock mass

quality improves, the PPV required for fragmenting and displacing the rock increases.

From the records of the particle velocity measured over time, frequency spectrum graphs

were derived employing the fast Fourier Transform (FFT). The peak frequency and

frequency ranges obtained in this way indicate that there is a strong relationship between

frequency ranges and rock mass quality, where high frequencies are undetectable and/or

decay more rapidly with decreasing rock mass quality.

4

In an attempt to reduce the large scatter of the recorded PPV versus SD data, a

modification and improvement to the Hustrulid-Lu method (Hustrulid and Lu, 2002) used

for the near-field PPV prediction, was made by the incorporation of geophysical

components into the proposed methodology. This methodology and the result of it, the

developed modeling tool utilizes a waveform seed generator to determine the peak

velocities of individual packets that pertain to a single blasthole of the round. PPV for

each blasthole can then be calculated from the linear superposition of all individual

packet waveforms whose phases are shifted by their respective arrival time differences,

that is, when they arrive at the geophone location. The methodology takes into account

the travelled distance, and the travelled time of the seismic wave (between the packet

centroid and the geophone), which differs for each packet. The methodology also takes

into account the vibration frequency of the given rock mass which has an effect on the

waveform generated. These three considerations should lead to greater accuracy in the

determination of the final PPV values.

The properties and characteristics employed in the model are as follows: the location,

length, and diameter of every blasthole in the round with respect to the geophones

location; the explosives linear charge density and VOD; the rock mass mediums body

and surface wave velocities and its main resonant frequency; and, the travelled length of

the wavefront comprising every individual packet originating at the blasthole. In

principle, only the shortest path travelled by the seismic vibration, measured from the

packet location to the geophone location, would generate the PPV and any other path

would merely add to the residual portion of the original particle velocity.

As a result of the frequency content analysis, the importance of analyzing the combined

particle velocity determined for a single blasthole from the combination of a wide range

of frequencies can be recognized, however, to simplify the analysis performed, only a

single predominant resonance frequency was used. To ascertain the models capabilities,

an example of a waveform generated from the linear superposition of a range of

waveforms each with a different frequency, was conducted and documented.

The implemented model was constructed keeping in mind that the seismic wavefront

originating at the packet location travels through a body of rock at the body wave

5

velocity, and once it has reached the face-wall contact of the blasting round, the

wavefront passes through a point of diffraction (POD); from there on, it travels through

the surface of the drifts wall, at the surface wave velocity, to the geophone location. In

the proposed methodology, of the two decomposed PPV vectors, the vector parallel to the

wall, and, the vector perpendicular to the wall (i.e., the vertical projection of the original

PPV vector before it passes through the POD), only the PPV magnitude of the vector

parallel to the wall is accounted for, while the other, the PPV magnitude of the vector

perpendicular to the wall, is discarded. This was done by the application of a factor to the

length of every packet ray trajectory. This factor is a function of the incidence angle of

the packets trajectory to the POD, explained in more detail below.

1.4 Statement of Contributions As a result of the field investigation and subsequent analysis of the data gathered, graphs

of PPV versus SD were developed for a wide range of rock mass qualities (Figure 4.38

and Figure 4.40). In addition, the corresponding average overbreak determination is also

provided for each of the mine sites investigated. These graphs were obtained using

existing methodologies but the innovation lies in the fact that the PPV versus SD relations

were obtained for a broad range of rock mass qualities, varying from fair/poor to

extremely competent and these empirical relations are combined into a single graph from

which the importance of rock mass quality on the PPV versus SD relations is emphasized.

Also, a set of graphs showing the content of resonance frequencies (Figure 4.10, Figure

4.19, Figure 4.28, and Figure 4.37), obtained from the particle velocity versus time

records, provides additional evidence of the strong relation existing between resonance

frequencies and rock mass quality. The main resonance frequency is also used as an input

parameter for the proposed methodology to determine PPV.

The primary contribution of this research is to present a new semi-empirical methodology

to determine PPV at any given location from any particular blasthole of the round. This

methodology was especially designed for a drifting situation and includes analytical

formulations (Eq. 41 through Eq. 45) and the development of a computer based modeling

tool. This computing tool was validated and tested using spreadsheet software, and

applied to determine PPV values at any distance from a given blasthole location. The

6

model takes into consideration the arrival times of a number of individual packets

forming the blasthole column, as well as the predicted path of the seismic wavefront. In

certain cases, the seismic wave diffracts at the face-wall contact and this phenomenon is

also incorporated into the new methodology. The specifics are explained in detail in

subsequent sections.

In summary, the provided empirical data relating PPV, SD, overbreak, and resonance

frequency with rock mass quality constitute valuable information to the reader for whom

similar rock mass condition could be present at their sites. In addition, the new

methodology proposed to estimate PPV and subsequently the validation and testing of the

modeling tool developed, may have a noteworthy positive impact on safety, as well as on

cost optimization of drift developments, both being key factors in underground mine

operations.

1.5 Thesis Outline The manuscript has been divided into 9 main chapters and a brief summary of each one is

given as follows:

Chapter 2 Literature Research, presents the theory and background of the main aspects

this thesis is focused on, particularly rock blasting and rock mechanics. It describes

crucial aspects with regard to PPV, rock mass quality, overbreak, and frequency

spectrum. A discussion of limitations of current methodologies follows, as they are

employed to assess near-field PPV, close to the blastholes perimeter, and also in the

intermediate- and far-field case. Also, the scarce number of alternative methods that can

be used on a regular basis, other than seismic monitoring, to assess damage caused by an

explosive charge of known properties and its relation to the quality of the rock mass, will

be addressed. The analytical and applied background regarding ground vibrations, wave

theory, seismic monitoring, particle velocity, damage potential, SD, near- and far-field

PPV prediction, frequency spectrum, and rock mass quality is also covered in this

chapter.

Chapter 3 Field Data Collection and Analysis , describes the procedures and processes

involved in the data acquisition and analysis of field measurements. The characteristics of

7

the equipment employed are described, as well as the processes of data gathering

including examples of a typical rock mass quality logging sheet, a laser scanner profile, a

structural mapping record, particle velocity and vector sum versus time records, and a

plot of frequency spectrum, among others. The ELOS concept is introduced, normally

applied to the determination of the average overbreak thickness of large open stopes, but

employed here for drift development type excavations. An example is also presented, of

the scatter that could be found in the delay time of pyrotechnic detonators, along with an

example of a PPV versus SD graph recorded for a given rock mass quality.

Chapter 4 Case Studies, presents details of the information gathered at the four mines

investigated including their locations, a brief description of the mining methods

employed to extract the ore, the types of ore and rock types under investigation, as well

as plan views of the monitoring area, and general descriptions of rock mass quality

including pictures of the rock mass conditions and the support system being employed.

Results of the analysis of the gathered data, PPV versus SD charts, are presented along

with best-fit curves and equations obtained from the point cloud of the recorded data,

including the range of frequencies at which a particular rock mass vibrates.

Chapter 5 PPV Modeling The Proposed Methodology, presents the methodology itself

including a new set of analytical equations to determine PPV at any location in the

vicinity of a blasting round, either at the face where the detonation of the blastholes

occurs, or on the walls some distance away from the blast. Details of the semi-empirical

modeling tool, including the geophysical and analytical background, are also presented.

The geophysical and analytical background provides the working ground for the analysis

of the data gathered in the field campaigns, as was presented in Chapter 4 Case Studies.

Validation of the modeling tool against current methodologies is performed in this

chapter as well as a series of tests to determine potential applications for the model, e.g.,

PPV analysis based on different rock mass qualities.

Chapter 6 Model Testing, tests the proposed semi-empirical modeling tool on one of the

four mine sites visited by estimating PPV values and comparing them against the field

data gathered. Three-axial plots of the recorded PPV determined for each blasthole

location are compared against surface contour plots obtained via the modeling tool. No

8

statistical analysis was performed to compare the modeled and field data owing to the

fact that some of the properties and constants used in the model were obtained from

literature (due to cost constraints on the data acquisition in the field).

Chapter 7 Applications of the Proposed Model, proposes other potential applications for

the modeling tool, such as estimation of the PPV values in the boundaries immediately

adjacent to the explosive charge. The model can also be used, for example, to perform

PPV decay contour plots in the vicinity of blastholes loaded with different types of

explosives. The interaction between two or more charges could also be a part of potential

applications making use of the analysis of the modeling results. In this chapter the

limitations of the modeling tool are also provided.

Chapter 8 Conclusions, includes a summary of the main findings and the contributions

made by this research.

Chapter 9 Recommended Future Work, describes a number of ideas to implement in

future studies for the continuation of the research presented herein, in order to expand

knowledge in the field of rock blasting. A good portion of the ideas mentioned in this

chapter point toward improving the models capability and tackling its shortcomings (as

mentioned in Chapter 7).

9

2 LITERATURE RESEARCH

2.1 Falls of Ground A Latent Threat to Miners From time to time, news appears of miners trapped, injured, or becoming part of fatalities

statistics that flood the media. News of injuries is a main concern to the families and the

community, to the mine, the industry, industrial health and safety organizations, and the

public in general. So any effort toward reducing injuries in the workplace should be

forefront.

Figure 2.1 - Figure 2.3 show percentage injuries and fatalities in the U.S. mining industry

occurring in underground (conventional stoping and caving) mining during the period

2000-2011.

Figure 2.1 Percentage of underground mining injuries in U.S. classified by accident type (source: U.S. Department of Labor: Bureau of Labor Statistics (http://www.bls.gov/iif/, June 2011))

Figure 2.2 shows the percentage of fatalities that occurred in the U.S. in underground

mining for the same period.

10

Figure 2.2 Percentage of underground mining fatalities in U.S. classified by accident type (source: U.S. Department of Labor: Bureau of Labor Statistics (http://www.bls.gov/iif/, June 2011))

Figure 2.3 shows the total number of injuries related only to fall of roof and fall of

face/rib/pillar that occurred in the U.S. during the period January 2000 to June 2011.

11

Figure 2.3 Fall of ground related injuries in U.S. (source: U.S. Department of Labor: Bureau of Labor Statistics (http://www.bls.gov/iif/, June 2011))

The information provided in the previous figure was obtained from the Accident Injuries

Data Set database. This information was filtered to show only conventional stoping and

caving underground mining methods, from which only injury records classified as fall of

roof or back and fall of face/rib/pillar/side/highwall is reflected. Underground locations

include faces, intersections, vertical, sloping and inclined shafts, underground shops and

offices, and others. Coal mining including shortwall, longwall, and continuous miner

methods do not form part of the data analyzed as they bear little relation to the drilling

and blasting techniques under study.

2.2 Ground Vibrations and Damage Assessment

2.2.1 Introduction

It is widely understood that the degree of damage sustained by a given rock mass as a

result of blasting is proportional to the quality of that rock mass (Bieniawski, 1989;

Barton et al. 1974; Hoek et al., 1980) as well as proportional to the quantity of explosives

fired per delay. Logically, the higher the quantity of explosives fired per delay, the higher

12

the resultant seismic vibration, and this vibration has a direct effect on the magnitude of

the damage sustained by the rock mass.

Given that it is nearly impossible to take measurements of peak vibration levels in the

immediate vicinity of a given blasthole, i.e., where the greater damage to the rock

actually occurs, these vibration levels have always been estimated by extrapolating

measured vibrations at considerable distances from the source. From statistical and

physical points of view, the greater the distance from the blast that data points are used

for extrapolation, the greater the error generated, thus the lower the reliability of

predicting the peak vibration levels responsible for the damage to the rock mass. This is

probably the greatest shortcoming of most of the research undertaken so far in this area,

and there are several relevant examples (Dey, 2004; Adamson et al., 1999, Murty et al.,

2003). Moreover, those who have attempted to monitor vibration levels nearer to a given

blast, have not done so for more than a single rock mass quality. Notably, for some of the

research undertaken, the methods employed require extra or special operations, such as

drilling perpendicular to the strike direction of the drift, which generally conflict with

production schedules, and for this reason, are not used on a regular basis. Boreholes for

instrumentation drilled in a different orientation than the blastholes, in many cases require

bringing in other drilling equipment, and even though they can prove to be useful, the

extra setup time may not allow the mining cycle to fit the constraints of the shift. On the

other hand, the installation of blast monitoring instrumentation can operate during parts

of the mining cycle where they produce insignificant interruptions to the operation.

In Murty (2003), peak vibration levels were predicted in the near-field, at a distance of

1m from the blast, while the nearest actual measurements were taken at a distance of 43m

from the blast. On the other hand, some research involving single blasthole firing has

attempted to monitor in the near-field using experimental rather than real-world mine

drift developments (Yang et al., 1994). Yang employed accelerometers rather than the

more direct measurement method utilizing geophones, requiring subsequent integration

of the acceleration versus time records in order to derive the corresponding particle

velocity, which involves an implicit approximation error as well as the use of a much

higher frequency band (accelerometers) to record the seismic data.

Documents

QUANTIFYING THE EFFECT OF ROCK MASS QUALITY ON PEAK PARTICLE VELOCITY FOR UNDERGROUND DRIFT DEVELOPMENT